Sputtering targets are used in the formation of semiconductor substrates as a source of material to be deposited on the substrates. In some applications layers of alloys composed of one or more metals are deposited onto the surface of a substrate to improve performance and characteristics of individual products. For example, magnetron sputtering is a widely used method to deposit thin layers of aluminum and non-aluminum metal alloys onto flat and patterned substrates. The fabricated substrates are then used in the manufacture of products such as integrated circuits, memory storage devices, magnetic recording or reproducing apparatus, and ink-jet heads.
Metals to be deposited on a semiconductor substrate are removed from the sputtering target by a plasma. The quality of the resultant semiconductor substrate depends on the quality of the sputtering target supplying the material, which in turn depends on the quality of its fabrication. The fabrication of the sputtering target, in particular the target composition and structure, is important in achieving a high performance, high density substrate.
Improperly fabricated sputtering targets have several undesirable features such as low density, the presence of intermetallic compounds, and a non-uniform composition. Low density sputtering targets are undesirable because they cause outgassing during pumpdown, where air trapped in the target either increases the time for the desired level of vacuum to be reached, or prevents the necessary vacuum from being reached at all, thus reducing uptime of the target. Additionally, impurities in the air trapped in the target can contaminate the film. Intermetallic compounds are brittle and may result in sputtering target failure during fabrication or operation. A non-uniform composition of the sputtering target is undesirable because it reduces the substrate yield, since the non-uniform composition is reproduced on the film coating the substrate.
One method of solving the problem of improperly fabricated or nonhomogeneous sputtering targets, and hence the problem of reduced substrate yield, has been to use separate targets as sources for the aluminum and the non-aluminum metal. This method, however, is inefficient in that the sputtering targets must be mechanically rotated to average out the composition from each metal. Additionally, mechanical rotation has only been used when the non-aluminum metal was tantalum, thus its applicability to non-aluminum metals other than tantalum is unknown.
It would be advantageous to fabricate a sputtering target that is a homogeneous composition of an unreacted aluminum and non-aluminum metal and that contains greater than about 2% to 5% by weight of aluminum. This would be sufficient to allow formation of an aluminum layer around the non-aluminum metal. Therefore, a high quality, high performance, substantially uniform sputtering target, and an efficient method of fabricating such a target, is needed.